Skip to main content

Full text of "The manufacture and properties of iron and steel"

See other formats

342                           METALLURGY  OE  IROF  AND  STEEL.
"For the purpose of determining this elastic limit let the testing machine be run by hand until the limit is passed and the record taken (or run by hand between the load of 30,000 pounds and the elastic limit), and then let the power gear be thrown in and the test completed in the present rapid fashion. Since the term 'yield point' is quite recent, and has no meaning essentially different from the words 'elastic limit' in time-honored practice, why need it be used at all?"
These conclusions represent common sense in their summary dealing with the petty theories of enthusiasts, who are so wrapped Up in the accurate determination of a micrometrical measurement that they ignore the-ftiore important variations inherent in the method itself, not to mention the still more overwhelming differences caused by changes in the history and shape of the material. I do not see, however, why it is necessary to drive a machine by hand. This is a confession of lack of ingenuity which is not credi-' engineering science.
SEO. XVIn:—Variations in the pulling speed.—To find the effect o:f variations in pulling speed, ten different rivet rods were taken from,:an acid open-hearth heat. From each rod five bars were cut, and. each! one was broken at a different speed. Table XVI-X shows that a decrease in pulling speed is accompanied by a decrease in ultimate strength, elastic limit, elastic ratio, and elongation. The differences are not extreme, but their regularity makes the testimony almost conclusive. In the slowest speed there is an exception to this rule in a marked increase of extension, and inspection shows that this does not arise from an average of erratic members, but from an increase in every bar. This point is not of great importance, since it requires nearly an hour to break a bar of steel at this speed. The reduction of area remains practically constant throughout the series. The natural result of this investigation would be a tendency toward higher breaking .speeds, but this may be carried too far, since with fast work it is more difficult to' take accurate readings.